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Microstepping MForce PowerDrive Manual Revision R032008
Motor Settings Screen (PWM Current Control)
The Motor settings screen allows the user to fine tune the settings of the PWM to optimize the current output for
a variety of stepping motors.
There are four parameters that may be set:
PWM Mask
PWM Period (Duty Cycle)
PWM Frequency Range
PWM Control
PWM Mask
The PWM mask parameter prevents the premature end of the forward period caused by switching transients
when the motor phase current is at low levels. Adjusting this value can impact the zero-crossing performance
of the motor. If experiencing the “tick” which is inherit in stepper motor systems, this may be minimized or
eliminated by adjusting this value. The range of this value is 0 to 255d and will be entered as a decimal value.
The Mask will act as a filter on the PWM signal to allow time for any ringing in the output circuitry to settle.
This range represents a 8-bit Hex value that specifies the Bridge Reverse Measure Time (REVTM) and the
Minimum Bridge Forward On Time (FORTM) ranging from 600 nS to 3.4 µS each (see table and diagram
below). Typically these values would be balanced. The table below shows the decimal value for each time.
Note that these are typical values and the currents may be unbalanced to fine tune the motor performance.
The default value for this parameter is 204 (0xCC), which represents a Reverse Measure Time and Minimum
Forward On Time of 2.5 µS.
Reverse Measure Time/Minimum Forward On Time
Hex Time Hex Time Hex Time Hex Time
0x0 600 ns 0x4 1.0 µs 0x8 1.6 µs 0xC 2.5 µs
0x1 700 ns 0x5 1.1 µs 0x9 1.8 µs 0xD 2.8 µs
0x2 800 ns 0x6 1.2 µs 0xA 2.0 µs 0xE 3.1 µs
0x3 900 ns 0x7 1.4 µs 0xB 2.2 µs 0xF 3.4 µs
Table 2.6.6: PWM Mask Settings
1.
2.
3.
4.
PWM Mask
PWM Frequency Range
PWM Period
(Duty Cycle)
Control Bits
Figure 2.6.13: Motor Settings Screen
Reverse Measure Time Min. Forward On Time
1 1 0 1 1 1 0 1
0xD (2.8 µS) 0xD (2.8 µS)
0xDD
PWM Mask Value = 221
Convert to Decimal
Figure 2.6.14: PWM Mask Bits